Defect Structures Introduced in FCC Metals by High-speed Deformation

Abstract

Variation in defect microstructures introduced by compression of three fcc metals, Al, Cu and Ni, was investigated over a wide range of strain rate, from 10 m 2 to 10 6 /s. Dislocations formed under high-speed deformation are randomly distributed, whereas dislocations formed under low-speed deformation develop into cell structures, the transition between the two being at a strain rate of 10 3 . Dislocations of opposite signs are equally mixed in high-speed deformation, whereas grouped dislocations in low-speed deformation are composed of unbalanced numbers of dislocations of opposite signs. In high-speed deformation vacancy clusters are formed at high density all over the matrix, whereas in low-speed deformation only a few numbers of vacancy clusters are formed in the area of localized distribution of dislocations, the boundary between these two characteristics being at the transition of the nature of dislocation distribution. In the high-speed deformation vacancy clusters are formed by the aggregation of deformation-induced vacancies, whereas in low-speed deformation they are produced directly by dislocation reaction during deformation. Stress during high-speed compression has been estimated to increase to more than 10 GPa. A model of plastic deformation that produces vacancies at high concentration is proposed, in which high-speed plastic deformation proceeds without involving dislocations.